A Question for Muslims: what kind of sin is it to stand in silent tribute ?

Em ... as for the question(s), I think simple words / facts will be wonderful enough. ( And I know that he later on published an announcement online that he also denounces those violent and terrorist acts of the Kunming 3.1 killings. )

[1] In Islamic religious beliefs, is standing in silent tribute for the deceased of other religious beliefs / atheism, a sin ? (Yes/No)

[2] If so, how bad is it ? Based on which part of the Koran ?

[3] If so, is avoiding funerals / memorial services for people of other religious beliefs / atheism an optimum choice for Muslims ?

[4] If so, and if a Muslim somehow ends up in a funeral / memorial service for people of other religious beliefs / atheism, what do you think is most appropriate to say to the family of the deceased ?